<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        /*calc支持长度值运算 + - * / 运算符前后都要空一格 */
        .div1{
            width: calc(100% - 100px);
            height: 100px;
            background: chocolate;
        }
        .div2{
            width: calc(100% / 3);
            height: 100px;
            background: crimson;
        }
    </style>
</head>
<body>
    <h1>qweqweq</h1>
<div class="div1"></div>
<div class="div2"></div>
</body>
</html>